module GeoHash

geohash.rb Geohash library for pure ruby Distributed under the MIT License

Constants

BASE32
BITS
BORDERS
NEIGHBORS
VERSION

Public Class Methods

adjacent(geohash, dir) click to toggle source

Calculate adjacents geohash

# File lib/pr_geohash.rb, line 66
def adjacent(geohash, dir)
  base, lastChr = geohash[0..-2], geohash[-1,1]
  type = (geohash.length % 2)==1 ? :odd : :even
  if BORDERS[dir][type].include?(lastChr)
    base = adjacent(base, dir)
  end
  base + BASE32[NEIGHBORS[dir][type].index(lastChr),1]
end

decode(geohash) click to toggle source

Decode from geohash

geohash: geohash code
return: decoded bounding box [[north latitude, west longitude],[south latitude, east longitude]]

# File lib/pr_geohash.rb, line 22
def decode(geohash)
  latlng = [[-90.0, 90.0], [-180.0, 180.0]]
  is_lng = 1
  geohash.downcase.scan(%r./) do |c|
    BITS.each do |mask|
      latlng[is_lng][(BASE32.index(c) & mask)==0 ? 1 : 0] = (latlng[is_lng][0] + latlng[is_lng][1]) / 2
      is_lng ^= 1
    end
  end
  latlng.transpose
end

encode(latitude, longitude, precision=12) click to toggle source

Encode latitude and longitude into geohash

# File lib/pr_geohash.rb, line 37
def encode(latitude, longitude, precision=12)
  latlng = [latitude, longitude]
  points = [[-90.0, 90.0], [-180.0, 180.0]]
  is_lng = 1
  (0...precision).map {
    ch = 0
    5.times do |bit|
      mid = (points[is_lng][0] + points[is_lng][1]) / 2
      points[is_lng][latlng[is_lng] > mid ? 0 : 1] = mid
      ch |=  BITS[bit] if latlng[is_lng] > mid
      is_lng ^= 1
    end
    BASE32[ch,1]
  }.join
end

neighbors(geohash) click to toggle source

Calculate neighbors (8 adjacents) geohash

# File lib/pr_geohash.rb, line 56
def neighbors(geohash)
  [[:top, :right], [:right, :bottom], [:bottom, :left], [:left, :top]].map{ |dirs|
    point = adjacent(geohash, dirs[0])
    [point, adjacent(point, dirs[1])]
  }.flatten
end